The present invention relates to orientation control materials for block copolymers used in directed self-assembly applications, and more specifically orientation-control materials for high-chi (χ) block copolymers prepared by ring opening of cyclic carbonate monomers.
Block copolymers (BCPs) find many applications in solution, bulk and thin films. Thin film applications of BCPs are particularly attractive for nanolithography and patterning due to the ability of some BCPs to form periodic self-assembled structures ranging in feature size from 5 nm to 50 nm. The thin-film self-assembly property of BCPs can be utilized with existing photolithographic techniques to provide a unique approach to long range order for semiconductor applications. This approach, called directed self-assembly (DSA) of block copolymers, promises to extend the patterning capabilities of conventional lithography.
BCPs for directed self-assembly (DSA) applications comprise two or three polymer blocks that can phase separate into domains characterized by ordered nanoscopic arrays of spheres, cylinders, gyroids, and lamellae. The ability of a BCP to phase separate depends on the Flory Huggins interaction parameter chi (χ). Polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is the most widely used block copolymer for DSA. For PS-b-PMMA block copolymers, perpendicular orientation of BCP lamellar domains is obtained by forming a layer of the BCP on an orientation control layer followed by annealing the BCP thin film to induce phase separation. Typically for PS-b-PMMA the orientation control layer is a crosslinkable or a brush-type random copolymer formed with styrene and methyl methacrylate. The neutrality of the orientation control layer (underlayer) can be controlled by adjusting the composition of styrene and methyl methacrylate in the final crosslinkable or brush-type random copolymer to enable perpendicular orientation of the BCP.
The minimum half-pitch of PS-b-PMMA is limited to about 10 nm because of lower interaction and interaction parameter chi (χ) between PS and PMMA. To enable further feature miniaturization, block copolymers having a high interaction parameter chi between two blocks (“high-chi”) are desirable. Several block copolymers having high interaction parameter between the two blocks have been studied to obtain smaller feature sizes. Of particular interest are block copolymers comprising a block derived from ring opening of a cyclic carbonyl monomer from a reactive end-group on the first polymer block. Block copolymers derived by ring opening polymerization (ROP) of cyclic monomers (e.g., lactides, lactones, ethylene oxide) have been used to generate sub-10 nm feature size for patterning application.
For block copolymers where both blocks are synthesized by a vinyl polymerization reaction, the corresponding orientation control materials can be easily synthesized by free radical or controlled-radical polymerization techniques. However, for block copolymers where one block is synthesized by vinyl addition and the second block by ring opening polymerization, simple techniques like radical polymerization cannot be used to make random copolymers of the corresponding monomers.
There exists a need to develop crosslinkable or brush-type random copolymers as orientation control materials for block copolymers wherein one block is made by a vinyl addition reaction and the second block is made by a ring opening polymerization.